<!DOCTYPE html>
<html lang="zh-CN">

<head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>
        <style>
                 .black {
                        width: 100px;
                        height: 100px;
                        background-color: black;

                }

                .red {
                        width: 100px;
                        height: 100px;
                        background-color: red;
                }

                .blue {
                        width: 100px;
                        height: 100px;
                        background-color: blue;
                }
        </style>
</head>

<body>
        <div class="black"> </div>
        <div class="red"> </div>
        <div class="blue"> </div>

</body>

</html>